A. Field of Invention
The present invention generally relates to repeaters for use in a communications network. More particularly, the present invention is directed towards delaying the transmission of signals on a transmit channel of the repeater.
B. Description of Related Art
FIG. 1 illustrates a traditional repeater set 100, including a repeater unit 101 and a set of transceivers 102.sub.1-X. A repeater set 100 as shown in FIG. 1 may be designed for use in a communications network that conforms to the Institute of Electrical and Electronics Engineers ("IEEE") 802.3u standard for a 100 Megabit per second ("Mb/s") Ethernet communications network. A specification for a repeater set 100 in an IEEE 802.3u communications network may be found in the IEEE Standards for Local and Metropolitan Area Networks: Supplement to Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications, Media Access Control (MAC) Parameters, Physical Layer, Medium Attachment Units, and Repeater for 100 Mb/s Operation, Type 100BASE-T (Clauses 21-30), The Institute of Electrical and Electronics Engineers, Inc., 345 East 47th Street, New York, N.Y. 10017-2394, USA, 1995 ("IEEE 802.3u Standard"), which is hereby incorporated by reference.
Each transceiver 102.sub.1-X may be coupled to a physical medium such as a cable or a bus for the purpose of transmitting data onto the physical medium and receiving data from the physical medium. Each transceiver may be coupled to a physical medium via a respective medium dependent interface ("MDI") 103.sub.1-X that supports one of the physical signaling standards set forth in the IEEE 802.3u Standard.
Each transceiver 102.sub.1-X also has a set of receive channel RX.sub.1-X, transmit channel TX.sub.1-X, and control C.sub.1-X signals that are coupled to the repeater unit 101. The transmit channel TX.sub.1-X, receive channel RX.sub.1-X, and control C.sub.1-X signals for each transceiver 102.sub.1-X may conform to the medium independent interface ("MII") 104.sub.1-X set forth in the IEEE 802.3u Standard or another suitable interface.
In operation, one of the transceivers 102.sub.1 begins receiving data from a physical medium via the MDI 103.sub.1. The transceiver 102.sub.1 then begins to provide the received data to the repeater unit 101 via the receive channel signals RX.sub.1 on the MII 104.sub.1. The repeater unit 101 then transmits the data received from the first transceiver 102.sub.1 to all of the other transceivers 102.sub.2-X coupled to the repeater unit 101.
The repeater unit 101 performs this transmission over the transmit channel TX.sub.1-X signals of each MII 104.sub.2-X The transceivers 102.sub.2-X then transmit the data received on their transmit channels TX.sub.2-X onto a respective physical medium via a respective MDI 103.sub.2-X. Each MDI 103.sub.1-X may also be coupled to a piece of data terminal equipment ("DTE"), such as a computer, which sources information onto the MDI 103 and receives information from the MDI 103.
If more than one transceiver 102.sub.1-X receives data on a MDI 103.sub.1-X and provides the data to the repeater unit 101 on a receive channel RX.sub.1-X, the repeater unit 101 identifies that a collision is taking place. In response to detecting the collision, the repeater unit 101 causes a JAM message to be transmitted onto each MDI 103.sub.1-X. This may be achieved by providing a JAM message on the transmit channel TX.sub.1-X that is coupled to each of the transceivers 102.sub.1-X. Each transceiver 102.sub.1-X then propagates the JAM message onto a respective physical medium via the MDI 103.sub.1-X.
The IEEE 802.3u Standard specifies two classes of repeaters. Class I repeaters are defined as being:
A type of repeater set specified such that in a maximum length segment topology, only one such repeater set may exist between any two DTE's within a single collision domain. IEEE 802.3u Standard, Clause 27.1.1.3. PA1 A type of repeater set specified such that in a maximum length segment topology, only two such repeater sets may exist between any two DTE's within a single collision domain. IEEE 802.3u Standard, Clause 27.1.1.3.
Class II repeaters are defined as being:
The IEEE 802.3u Standard also defines the following parameters for a repeater set 100:
Start-of-Packet Propagation Delay ("SOP"): The delay between the start of a packet of data being received on a receiving transceiver's MDI to the start of the packet of data being transmitted on a transmitting transceiver's MDI. IEEE 802.3u Standard, Clause 27.3.1.3.3. PA0 Start-of-Collision JAM Propagation Delay ("SOJ"): The time delay between the start of the second packet in a collision arriving at the MDI of a transceiver and the start of the JAM message being transmitted onto the MDI of all transceivers. IEEE 802.3u Standard, Clause 27.3.1.4.3. PA0 Cessation-of-Collision JAM Propagation Delay ("EOJ"): The time delay between the end of a packet, which causes the repeater unit to cause the JAM message to no longer be transmitted by a transceiver, and the JAM no longer being transmitted on the MDI of the transceiver. IEEE 802.3u Standard, Clause 27.3.1.4.4.
For Class I repeaters, the sum of SOP and SOJ must not exceed 140 bit times, in order to comply with the IEEE 802.3u Standard. For Class II repeaters, the IEEE 802.3u Standard requires that the sum of SOP and SOJ must not exceed 67 bit times when the physical medium is 100BASE-T4 type. For Class II repeaters, the IEEE 802.3u Standard requires that neither SOP nor SOJ exceed 46 bit times in 100BASE-TX and 100BASE-FX physical medium types.
For both Class I and Class II repeater sets, such as repeater set 100, the IEEE 802.3u standard specifies that EOJ be less than or equal to SOP for each port in the repeater set. This requirement assures that the end of a collision JAM message is propagated to all DTE's on a communications network before a new packet of data is received by a DTE on the communications network. This prevents the new packet of data from merging with the JAM message and being corrupted.
Accordingly, it is desirable to have a mechanism for use with a repeater set that allows for balancing the SOP and EOJ delay parameters so that EOJ is less than or equal to SOP for each port of the repeater set.